The present invention generally relates to an apparatus and a method for degassing and preventing gelation in a viscous liquid used in semiconductor processing and more particularly, relates to an apparatus and a method for eliminating air and gelation in a viscous liquid of polyimide used in semiconductor fabrication processes.
In the fabrication of semiconductor devices, a semi-conducting wafer must be processed in a multiplicity of fabrication steps, i.e. as many as several hundred in order to produce the final finished product. These processing steps may include etching, cleaning, deposition and various other processing procedures. A variety of chemicals, including liquids and gases may be used in the processing steps wither to etch a specific feature on the IC chip, to clean after certain processing steps, to deposit layers from reactant chemicals, or to carry out other necessary processing steps.
For instance, in photomasking and metal cleaning processes, a variety of speciality chemicals are used. An important consideration in the usage of such speciality chemicals, i.e. photoresists, developers, spin-on-glass and polyimide is the transporting and storage of the materials. In the case of a photoresist material, the photosensitivity and the shelf life of the material depends on its storage temperature. It is important to maintain such material within a range of 5xc2x0 C. to 20xc2x0 C. for a photoresist/developer and xe2x88x9220xc2x0 C. to 10xc2x0 C. for spin-on-glass/polyimide materials.
The transporting of these speciality chemicals, especially liquids, or the delivery from a storage reservoir, i.e. a holding tank or a buffer tank, to a processing chamber where the liquid is used is another important aspect of the fabrication process. A process liquid, such as a photoresist or a developer, can be transported in a fluid passageway of a stainless steel tubing assisted by an electrical pumping means. One of such conventional liquid delivery system for a polyimide passivation material is shown in FIG. 1.
FIG. 1 illustrates a conventional polyimide dispensing system 10 which utilizes compressed air in conduit 12 and valve 14 to exert a positive pressure in the source tank 16 such that a sufficient amount of a polyimide liquid 18 is applied to the reservoir tank 20 through conduit 22 and valve 24. The valve 14 is an open/closed valve for controlling the air pressure in conduit 12. Valve 14 is open when polyimide solution is requested from the reservoir tank 20 via master controller 30. Valve 14 is closed when no request is sent from reservoir tank 20. A sensor 26 is further provided for sensing the presence of a polyimide liquid in conduit 22. When the source tank 16 becomes empty, compressed air is drawn into the conduit 22 and activates the sensor 26 which then sends an alarm signal to the operator for refilling the source tank 16 with new polyimide solution. The sensor 26 can be an optical type which senses an intensity change of a refracted light as air enters the conduit 22. The function of valve 24 is the same as valve 14 which is open or closed at the same time to supply polyimide into the reservoir tank 20.
The reservoir tank 20 is a buffer tank for the polyimide solution 18. The major function for the reservoir tank 20 is to degas and to remove gel that flows in from the conduit 22 or the source tank 16. The sources of bubbles or gel may be of many different kinds, i.e. from the polyimide material itself during the fabrication of the material; from the conduit 22 during the replenishment of the source tank 16; or from the open/closed action of valve 24 during the operation of the polyimide dispensing system 10.
The reservoir tank 20 is equipped with four different sensors 28,32,34 and 36 for maintaining a suitable solution level in the tank. The level of the solution should be kept between the high sensor 32 and the low sensor 34. When the solution level is sufficiently low as to activate the low sensor 34, the low sensor 34 sends a signal to the master controller 30. The master controller 30 then controls valves 14 and 24 to refill the reservoir tank 20, and stop the refill action as the high sensor 32 is activated by the level of the solution. A second high sensor 28 is an overflow sensor which functions when the first high sensor 32 malfunctions to drain the excess solution from drain pipe 38. The low sensor 36 provides an interlock function when the solution level is sufficiently low to activate the low sensor 36 in order to prevent air from entering the outlet conduit 40 and the dispensing pump 42.
The dispensing pump 42 is normally provided in a dual- stage pump, i.e. such as a MILLIPORE(copyright) Photo-250 Pump, equipped with an internal filter (not shown). The dispensing pump 42 extracts the polyimide solution along conduit 40 from the reservoir tank 20 while filtering out contaminants such as bubbles and gel by the internal filter. The dispensing pump 42 then delivers the polyimide solution along conduit 44 for dispensing to wafer 46 through a dispensing nozzle 48. The wafer 46 is positioned on a wafer platform 50 by a vacuum means and spins by platform 50 during the polyimide spin coating process.
Under normal processing conditions, some bubbles will be found in the reservoir tank 20 and in the conduits 22 and 44. A complete polyimide flow takes place from the reservoir tank 20, through the conduit 40, the dispensing pump 42, the conduits 44 and 52 and the liquid feed conduit 60 by trapping a limited number of air bubbles by the internal filter provided in the dispensing pump 42. At the same time, a three-way valve 54 is utilized to divert a polyimide solution from conduit 44 to the conduit 52, while cutting out the solution flow in conduit 56. The recycled flow is used to save the usage of the polyimide material. The operation of the sensor 26, the valves 14,24 and 48, the dispensing pump 42 and the wafer platform 50 is controlled by the master controller 30, which is normally a micro-processor.
The conventional viscous liquid dispensing system 10, shown in FIG. 1, while capable of stopping, by filtering out, some of the air bubbles trapped in the liquid, is not efficient in filtering out, or removing all the air bubbles. Furthermore, during the dispensing of a material such as polyimide for passivation of an IC device, a premature reaction or sometimes known as xe2x80x9ca dark reactionxe2x80x9d occurs in the polyimide liquid between the monomer and the initiator such that undesirable gel is formed. When the gel is dispensed onto the wafer surface, serious quality problems in the passivation layer occurs. An improved viscous liquid dispensing system is therefore desirable for dispensing a highly viscous liquid such as polyimide to not only degas the liquid by eliminating air bubbles, but also to prevent the formation of gel in the liquid.
While it has been found that oxygen, when contained in a polyimide solution prevents or retards the gelation process, there is little possibility that oxygen can be added to a polyimide solution in the conventional dispensing system. For example, the liquid feed conduit 60, shown in an enlarged, cross-sectional view in FIG. 1A, does not allow an extended, prolonged exposure of polyimide with air, which contains approximately 20% oxygen. As shown in FIG. 1A, the liquid feed conduit 60 is normally provided with a sharpened tip portion 62 to facilitate a polyimide flow 64 into the solution 18. While attempts have been made to increase the distance between the tip portion 62 and the liquid level 66, other undesirable processing difficulties are caused by an impact between the liquid flow 64 and the liquid level 66, resulting in a more severe air bubble problem. It should be noted that, for simplicity reason, the liquid output conduit 40 and the drain pipe 38 are not shown in FIG. 1A.
It is therefore an object of the present invention to provide an apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank by eliminating a straight-tube type liquid feed conduit.
It is a further object of the present invention to provide an apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank by using a J-shaped liquid feed conduit.
It is another further object of the present invention to provide an apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank by utilizing a liquid feed conduit configured in a J-shape such that the exposure time of the liquid to ambient air is increased.
It is still another object of the present invention to provide an apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank by providing a liquid feed conduit having a J-shape and a wave-form exterior surface on the outlet of the conduit to further increase the exposure time of the liquid with ambient air.
It is yet another object of the present invention to provide an apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank by providing a specially configured liquid feed conduit such that the exposure time between the liquid and ambient air can be increased by at least two-fold.
It is still another further object of the present invention to provide a fluid reservoir tank for holding a viscous liquid therein and for eliminating air and gelation in the liquid by utilizing a liquid feed conduit that is formed in a J-shape having a bottom U-section immersed in the liquid.
In accordance with the present invention, an apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank is provided.
In a preferred embodiment, the apparatus for degassing and preventing gelation in a viscous liquid stored in a liquid reservoir tank is provided which includes a reservoir tank that has a cavity therein for holding a viscous liquid; a liquid feed conduit of J-shape that has an inlet end at a top of a first vertical section in fluid communication with a liquid source and an outlet end at an opposite end of a second vertical section of the J-shaped conduit protruding above the liquid, a U-section of the conduit is generally immersed in the liquid; and a liquid output conduit that has an inlet end immersed in the liquid and an outlet end in fluid communication with a dispensing nozzle of the liquid.
In the apparatus for degassing and preventing gelation in a viscous liquid stored in a reservoir tank, the outlet end of the liquid feed conduit further includes an exterior surface configured in a curvilinear form, the outlet end may further include an exterior surface configured in a wave-form, or in a sawtooth form. The outlet end of the liquid feed conduit may further include an exterior surface that is at least twice the interior surface of the conduit. The liquid feed conduit of J-shape may be constructed of a first vertical portion of a first length, a second vertical portion of a second length smaller than the first length, and a U-shape section connecting the first vertical portion and the second vertical portion together providing fluid communication therethrough. The outlet end of the liquid feed conduit of J-shape is at least 2 cm shorter than the inlet end. The first length of the first vertical section is at least 2 cm longer than the second length of the second vertical section. The liquid feed conduit may be formed of a corrosion-resistant material, or may be fabricated of a corrosion-resistant polymeric material. The reservoir tank may further include an overflow drain pipe for preventing overfilling of the tank. The apparatus may further include a pump means situated in-between the outlet end of the liquid outlet conduit and the dispensing nozzle.
The present invention is further directed to a fluid reservoir tank for holding a viscous liquid therein and for eliminating air and gelation in the liquid which includes a tank body that has a cavity therein for holding a quantity of the liquid; a liquid feed conduit formed generally in a J-shape that has a first vertical section and a second vertical section connected in fluid communication by a bottom U-shaped section, the first vertical section has an inlet end connected to a liquid source, the second vertical section has a length smaller than the first vertical section and an output end for overflowing the liquid into the cavity while exposed above a surface of the liquid in the cavity with the bottom U-shape section immersed in the liquid; and a liquid output conduit of a straight shape that has an inlet end immersed in the liquid juxtaposed to a bottom of the cavity and an outlet end in fluid communication with a dispensing nozzle for the liquid.
In the fluid reservoir tank for holding a viscous liquid and for eliminating air and gelation in the liquid, the outlet end of the liquid feed conduit may further include an exterior surface that is configured in a curvilinear form, or in a wave-form or in a sawtooth form. The exterior surface may be at least twice the interior surface of the conduit. The second length of the second vertical section may be at least 2 cm shorter than the first length of the first vertical section. The liquid feed conduit and the liquid output conduit may be formed of a TEFLON (tetra-fluoro-ethylene) material. The system may further include a pump means connected in fluid communication between the outlet end of the liquid outlet conduit and the dispensing nozzle.